Before we dive in, you don't want to make your Clan exactly like RiverClan (no pun intended). Example: You come up with a Clan called CreekClan who love to swim and fish. These cats are also strong and live by a river. If you were to do this, you're basically just bluntly paralleling an original Clan. If you are going to base your Clan off of an existing one, remember to be more original. For example, instead of being large and well-fed like RiverClan, your Clan can be quite small and sneaky, slipping silently through the waters. This makes CreekClan a lot more original and interesting to learn about.
The skills of your Clan is yet another key aspect that will make them stand out from other Clans, think carefully now! As I said before, territory reflects skill. If your Clan lives in a rocky high-altitude area, they will most likely be exceptional climbers and jumpers to maneuver around their rocky home. If your prefer swimming, your Clan might live near a ocean or river, and be skilled in the water. Be creative!